1. Field of the Invention
The present invention relates to an image adjusting apparatus which is capable of automatically adjusting a toner density on a copied image.
2. Description of the Related Art
The present inventors know an image forming apparatus such as a copying machine which includes an image adjusting apparatus. Such as the copying machine is, in general, arranged to have a defined toner density of a copied image. That is, the toner density is pre-defined in light of some factors of the components included in the copying machine, such as an exposing voltage of a copy lamp, a charging voltage of a charger and a developing bias voltage of a developer. For automatically adjusting the toner density of the copied image, therefore, it is possible to take the steps of measuring a toner density and an electric potential on a photosensitive body, deriving optimum voltage values based on the measured values, and controlling at least one of the above-mentioned voltages by referring to the corresponding optimum voltage.
In order to measure the toner density on the photosensitive body and derive a reference voltage of an exposing voltage of a copy lamp based on the measured toner density, for example, the forgoing image adjusting apparatus is arranged to measure a toner density of a sample by changing an exposing voltage, to obtain a relation between the exposing voltage and the toner density as a certain function such as a polygonal line approximation or a least square method and to derive a reference voltage so that the toner density may reach a predetermined value in light of the obtained relation. In this case, the relation between the exposing voltage and the toner density approximates to a linear function if the least square method is used.
However, in case of deriving the reference exposing voltage of the copy lamp base on the measured toner density on the photosensitive body for example, the relation approximating to the linear function such as the polygonal line may make the reference voltage erroneous if one of the samples has a too much dispersion. This results in disadvantageously disabling to adjust the toner density of the copied image accurately.
Further, if the forgoing image adjusting apparatus employs the least square method, the relation between the exposing voltage and the toner density is obtained as one kind of function. Hence, if the copying machine may provide two or more copying modes such as a photo mode for copying a photograph and a graphic mode for copying characters or graphics, the same function may apply to obtention of a reference voltage at any mode in such the image adjusting apparatus. This results in disadvantageously disabling to accurately adjust the toner density on the copied result at each copying mode.